Moose,
I ran a 12v switch into the cab that activates the coil of a relay. To this relay I hooked up 24v which the switch operates. As long as the amperage isn't greater than the relay can handle mixing and matching 12 and 24 volts across a relay isn't or shouldn't be a problem (I'm assuming decent relays - Bosch, Hella, etc...) I would definately switch the racor.
I found 24v off of the positive battery terminal and installed a fuse. My future plan is to install a 24v fuse panel (watertight) under the hood and make the install cleaner. Right now I have inline housed fuses on the 24v items.
I run this combination 24/12v relay stuff in 4 or 5 spots under the hood (starting, walbro, racor, a/c, ignition circuit) and haven't had a problem yet....
for what it's worth....
-mike